Fused yolk sacs in a case of forked cord of monochorionic di
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A healthy 29-year-old nulliparous woman visited at the 8th week of gestational age (GA) because her pregnancy self-testing was positive. Transvaginal ultrasound revealed two fetuses, each with their own active heartbeat, and both had their own amniotic membrane, thus suggesting an MDT pregnancy. One characteristic finding recognized was that two yolk sacs were completely fused, and the connecting stalks, which become the site of the future umbilicus, were also located in close proximity to each other. Subsequently, FC was recognized by a trans-abdominal ultrasound for screening at 16th GA, and no other abnormal findings were detected.

The pregnancy course was uneventful and healthy female babies, weighing 2,285g and 2,345g, were born vaginally at 36th GA. The umbilical and placental inspection revealed that each umbilical cord had two arteries and one vein, which fused at the proximity of the placental surface, where the amniotic
membrane divided each cavity. In this case, which is the third such case in the literature and survived with prenatal diagnosis, unique findings were that fused yolk sacs were observed with the amniotic membrane dividing two fetuses as early as 8th GA, in addition to the close location of both connecting stalks. From an embryological viewpoint, the folding of the embryo and expansion of the amniotic cavity bring the connecting stalk and yolk sac together to form the umbilical cord after 9th GA.

Source: https://obgyn.onlinelibrary.wiley.com/doi/epdf/10.1002/uog.22142